Otitis externa is an inflammation or infection of the external auditory canal, the pinna (auricle), or both. The disease can be a local condition (e.g., atopic dermatitis, food hypersensitivity, parasitic diseases, or seborrhea, etc.) or part of a systemic disease (e.g., food allergy, endocrinopathies, etc.). The disease arises from primary causes, such as foreign bodies, infections, parasites, glandular hyperplasia, etc., and secondary causes, such as bacteria, chemicals, and yeast. Usually secondary causes are complicating factors from a previously existing condition that can lead to otitis externa if one or more predisposing factors are present at the same time. For instance, predisposing factors are able to alter the ventilation of the external auditory canal, thus increasing the humidity and temperature of the external auditory canal (e.g., obstructive diseases such as neoplasms, frequent baths, swimming, abundant hairs inside the external auditory canal, pendulous pinna, hypertrichlosis, etc.). The presence of predisposing factors tends to be the cause of disease persistence, and untreated otitis externa can lead to irreversible changes of the external auditory canal, such as metaplasia and ossification, and the concomitant presence of otitis media. For these reasons, chronic otitis externa is a difficult disease to manage and treat.
One of the main aspects involved in the chronicity of the disease is the presence of infections caused by bacteria resistant to different antibiotics (e.g., Pseudomonas aeruginosa). To manage such conditions, usually, both topical and systemic long lasting (1 to 2 months) antibiotic treatments are needed, followed by anti-inflammatory drugs. Furthermore, in an occurrence of purulent discharge, the external auditory canal has to be rinsed and cleaned with specific detergents; otherwise topical antibiotics may be ineffective. Nevertheless, even with topical antibiotics, without solving the primary cause, the condition will inevitably relapse. Different surgical procedures are possible (e.g., from lateral ear canal resection to total ear canal ablation with lateral osteotomy of the tympanic bulla), but these procedures leave a permanent aftermath.
Otitis externa is a common inflammatory disease in mammals, such as humans, dogs, and cats. For instance, swimmers are particularly prone to otitis externa due to repeated exposure to water. Additionally, otitis externa afflicts up to 10-20% of dogs visited in a first opinion veterinary clinic.
Effective treatments of otitis externa and chronic or relapsing otitis externa are needed.